Role of Substance P in Post-Traumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a chronic, debilitating disorder that places a significant burden on individuals and society. Abnormalities in the serotonergic and noradrenergic systems and dysregulation of the hypothalamic-pituitary adrenal (HPA) axis have been proposed as neurobiological mechanisms in the development of the disorder, however the exact underpinnings of the neurobiology of the disorder must be elucidated. Distribution of substance P (SP) and its receptor, neurokinin 1 (NK1) receptor, includes regions implicated in the pathophysiology of PTSD, namely the amygdala, hippocampus, hypothalamus, and locus ceruleus. There is a considerable spatial (and therefore functional) overlap between the SP-NK1 receptor system and other neurotransmitter (e.g., norepinephrine, serotonin) pathways with well established roles in anxiety. Preclinical studies indicate that stress regulates levels of SP in several brain regions. In addition, in several animal models, NK1 receptor antagonists demonstrate anxiolytic-like property. These anxiolytic-like effects seem to involve different mechanisms than those of currently available anxiolytics. In this protocol, we will use a PET ligand that acts as an NK1 receptor antagonist, \[18F\]SPA-RQ (\[18F\]-labeled Substance P Antagonist Receptor Quantifier). Using this tracer, we will look for regional differences in NK1 receptor binding in 20 patients with PTSD and 20 healthy controls. The goal of the present study is to demonstrate the involvement of SP in PTSD, and thereby, further our understanding of its role in the psychopathology of this illness.